Adsorbent for desulfurization of sulfur dioxide containing waste gases

ABSTRACT

A carbon containing adsorbent for the desulfurization of carbon dioxide containing waste gases is impregnated with a mixed catalyst, the catalyst comprising (a) a vanadium compound and (b) at least one compound of the elements potassium, lithium or barium. The catalyst has considerably improved regeneration values.

United States Patent 1' Martin et al.

[ June 19, 1973 ADSORBENT FOR DESULFURIZATION OF SULFUR DIOXIDECONTAINING WASTE GASES [75] Inventors: Kruel Martin, Essen-Bergerhausen;

Dieter Zurawsky, Gladbeck; Harald Juntgen, Essen-Heisingen, all ofGermany [73] Assigneez Bergwerksverband GmbH, Essen,

Germany [22] Filed: Oct. 7, 1968 [21] Appl. No.: 765,690

[30] Foreign Application Priority Data Oct. 6, 1967 Germany P l6 19840.6

[52] US. Cl. 55/73, 55/74, 23/178 S [51] Int. Cl 801d 53/04, C0lh 17/51[58] Field of Search 55/387, 74, 522,

[56] References Cited UNITED STATES PATENTS 2,701,240 2/1955 Bregar210/502 X 3,327,859 6/1967 Pall 210/502 UX 3,396,122 8/1968 Brauer252/428 3,429,103 2/1969 Taylor 55/71 3,416,293 12/1968 Alexander 55/733,501,897 3/1970 Helmen et a1... 55/73 3,300,280 1/1967 Terminet 23/313,318,662 5/1967 Pauling 23/168 Primary Examiner-Charles N. HartAttorney-Michael S. Striker [57] ABSTRACT 9 Claims, No DrawingsADSORBENT FOR DESULFURIZATION OF SULFUR DIOXIDE CONTAINING WASTE GASESBACKGROUND OF THE INVENTION When SO -containing waste gases aredesulfurized by means of carbon-containing adsorbents, it is well knownthat the sulfur dioxide is not adsorbed as such but that a catalyticoxidation of the S to 50;, takes place at the surface of the adsorbentunder the action of the air which is present in the waste gases. The80;, is then hydrated immediately after its formation to H 80, by meansof the water vapor which is always present in the flue gas and isretained as such in the pores of the adsorbent. After saturation of theadsorbent with I-I SO which occurs at a concentration between 60 and 80weight percent in the pores, the sulfuric acid must again be removedfrom the adsorbent.

The desulfurization and consequent charging with sulfuric acid isfollowed up with a thermal treatment under exclusion of oxygen at atemperature from 400 to 600 C in order to effect a regeneration of thecarbon-containing adsorbent. The sulfuric acid in this case is reducedto S0 as appears from the following equatron There is thus obtained adesorption gas which is high in S0 and which in addition contains CO Nwater vapor and possibly some CO. The initial desulfurization activityof the material however deterioates substantially if the adsorbent ispassed in this manner through several adsorption-desorption cycles.

SUMMARY OF THE INVENTION The invention therefore has the object tomaintain the activity of carbon-containing adsorbents which are chargedat temperatures between 100 and 200 with S0 and H 80 respectively, andwhich are then subjected to regenerating treatments at temperaturesbetween 400 and 600C. A further objective is, if possible, to evenincrease the adsorption activity of the adsorbent. 7

These objects are solved by impregnating the carbon containing adsorbentwith a mixed catalyst, the catalyst comprising (s) a vanadius compoundand (b) at least one compound of the elements potassium, lithium orbarium.

The catalyst may contain in addition compounds of the elements aluminum,chromium, silicon or titanium. It may also contain a phosphorouscompound.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Any desired compounds of thelisted elements may be used in the mixed catalyst. Where the compoundsare in the form of water-soluble compositions, they are applied to thesurface of the adsorbents from an aqueous solution. To the extent thatthey are not watersoluble, they are applied from an aqueous suspension.Preferably, this is done by spraying the solution or suspension onto theadsorbents or also by means of a vacuum impregnation. The impregnatedadsorbent is then subjected to drying l l0ll 0C. As for the amounts ofthe compounds, it is preferred to use the vanadium compounds in anamount of 30-50 weight percent, while the compounds of the otherelements may be used in an amount between about 50 and 70 weight percent. However, other weight relations are also possible, such as 20 or80 20. In the last case, the mixed catalyst will contain a comparativelylarge amount of vanadium compound.

The compound of the elements lithium, potassium or barium, that is atleast one of these compounds, must be present in addition to the.vanadium compound. Additionally, it is preferred to further havepresent at least one element of aluminum, chromium, silicon or titanium.These latter compounds may have an effect as dispersing media.

The amount of mixed catalyst is up to about 15 weight per cent relativeto the untreated carboncontaining adsorbent. This amount is applied tothe surface of the adsorbent. It is 1 to select the amounts in a mannerthat the final adsorbent contains the vanadium element in an amount of 2weight per cent relative to the untreated adsorbent, and that the otherelements are added in a relation, expressed in their gram atomicweights, of 1 l 1 to the vanadium, such that the relation, for instance,is V K :A1= 50.95 39.096 29.97 (gram). Another feature of the inventionis the possible addition of phosphorous compounds to the catalyst. Theaddition of phosphorus, for instance in the form of (HPO has anadvantageous effect in regard to the use of the adsorbent since itinhibits the auto-oxidation of the adsorbent to a substantial extent,without imparing its desulfurization action.

The carbon-containing adsorbent may in the first place be activecharcoal. It may also be a so-called semicoke made from peat, lignite ormineral coal or preoxidized mineral coal. The specifications of theseadsorbents such as mean pore size and inner surface can be varied in awide range.

The following examples will further illustrate the invention.

EXAMPLE 1 A flue gas of the composition of 0.3 vol-% S0 3.0 vol-% 0 6.0vol-% H 0, and 90.7 vol% N was passed through a solid layer of cmadsorbent in an amount of 80 liters per hour. The layer had a thicknessof 50 cm, the residence time was 5 seconds. The adsorption temperaturewas 120C. The concentration of S0 was then measured at the inlet andoutlet from the adsorbent and the degree of activity or desulfurizationof the adsorbent layer was ascertained for each given period of timefrom the difference of the two S0 values. The measure for thedesulfurization activity was the time period during which the initialdesulfurization degree which was assumed to be 100 percent had decreasedto 90 percent. The limit value of the desulfurization therefore was 90percent related to time (in hours).

After charging the adsorbent with H 80, up to this limit, the adsorbentwas then reactivated in a gentle nitrogen flow for 4 hours at atemperature of 600C.

The basic material of the adsorbent was a bituminous coal ofa grain sizebetween 1 and 2 mm that had been activated with water vapor up to a lossof 28 weight percent.

The mixed catalyst was formed by dissolving or suspending 4.6 g NH VO4.4 g K 50, and 6.6 g Li SO, in about 50 ml water. The solution orsuspension was then applied, by spraying, to 94 g of carrier material.The material was subsequently dried at C. The total contents ofcatalytically active chemicals relative to the untreated adsorbentmaterial was as follows: 3.8 wt.-% V 2.6 wt.-% K 0 and 3.9 wt.-% L1 0.

The following Table proves that the initial activity decreases rapidlywith the untreated adsorbent while with the treated adsorbent it evenincreases during the proceedings.

TABLE I limit value for desulfurization 90% (11) Number of Carrieradsorptionmaterial with catalyst:

desorption without cycles catalyst V O ,-K O-Li,0 V O -K O-SiO 1 10.5 11.7 12.3 2 8.0 7.3 13.3 3 6.2 15.6 14.2 4 4.4 12.3 14.0 5 3.3 1 1 .714.7 6 4.2 12.2 14.6 7 4.2 13.4 14.7

EXAMPLE 2 A technical grade of active charcoal with a grain size ofbetween 1 and 3 mm was impregnated with a mixed catalyst in the mannerof Example 1, was charged with H 80 at 120C and was thermally treatedfor reactivation with a gentle nitrogen flow for fourghours at 400C.

The following Table demonstrates that the activity (measured again withrelation to the desulfurization limit value of 90 percent) was verysmall without a catalyst while it increased about 10 or times afterimpregnation of the catalyst.

A lignite, low-temperature coke that was activated with water vapor(burning loss 10 percent) was impregnated in the manner of Example 1with a mixed catalyst comprising 1 wt.-% each of vanadium, lithium andphosphorus and was subjected to charging at 200C with H 80 andreactivaton at 600C. The following Table shows the negative effect ofthe adsorption temperature in regard to the desulfurization activity.The efficacy of the adsorbent is, however, substantially increased byadding the catalyst.

TABLE I11 limit value for desulfurization 90% (It) Number of adsorption-Catalyst: desorption- Carrier material cycles without catalyst V;O,-Li,O-P,O,, 1 5.8 9.1 2 4.3 7.0

2.2 5.9 1.7 4.6 1.1 4.6 Without further analysis, the foregoing will sofully reveal the gist of the present invention that others can byapplying current knowledge readily adapt it for various applicationswithout omitting features that, from the standpoint of prior art, fairlyconstitute essential characteristics of the generic or specific aspectsof this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:

1. A process for increasing, maintaining or recuperat ing the activityof carbonaceous adsorbents, the said process comprising impregnating theadsorbent with a mixed catalyst, the said catalyst comprising a. avanadium compound,

b. at least one compound of an element selected from the groupconsisting of the elements potassium, lithium and barium,

c. at least one compound selected from the group of elements aluminum,chromium, silicon and titanium, and

d. at least one compound of phosphorus, wherein said vanadium compoundcomprises between 20 and 50 percent by weight of the total catalyst andwherein the balance of the other compounds in the catalyst comprisesbetween 50 and percent thereof and wherein the amount of vanadium is 2percent by weight relative to the weight of the untreated adsorbent andwherein the different elements in the compounds of the catalyst arepresent in a relation of l l as to each other element, expressed in gramatomic weights and then using the impregnated adsorbent in thedesulfurization of sulfur dioxide containing gases; followed bysubjecting the adsorbent thereafter to a thermal regeneration.

2. Process according to claim 1, wherein the vanadium compoundis-vanadium dioxide.

3. Process according to claim 1, wherein said compound at (b) isselected from the group consisting of lithium oxide and potassium oxide.

4. Process according to claim 1, wherein said compound at (c) isselected from the group consisting of aluminum oxide, chromic oxide andtitanium oxide.

5. Process according to claim 1, wherein the compound at (d) ismetaphosphoric acid.

6. Process according to claim 1, wherein said adsorbent is selected fromthe group consisting of active charcoal, semicoke and pre-oxidizedbituminous coal.

7. The process ofclaim 1, wherein the desulfurization is carried out ata temperature of about -200C.

8. The process of claim 1, wherein the adsorbent is regenerated in athermal regeneration at about 40()-6()OC.

9. The process of claim 1, wherein the catalyst is upplied to thesurface of the adsorbent in the form of an aqueous solution orsuspension in an amount up to 15 percent by weight relative to theweight of the untreated adsorbent.

2. Process according to claim 1, wherein the vanadium compound isvanadium dioxide.
 3. Process according to claim 1, wherein said compoundat (b) is selected from the group consisting of lithium oxide andpotassium oxide.
 4. Process according to claim 1, wherein said compoundat (c) is selected from the group consisting of aluminum oxide, chromicoxide and titanium oxide.
 5. Process according to claim 1, wherein thecompound at (d) is metaphosphoric acid.
 6. Process according to claim 1,wherein said adsorbent is selected from the group consisting of activecharcoal, semicoke and pre-oxidized bituminous coal.
 7. The process ofclaim 1, wherein the desulfurization is carried out at a temperature ofabout 100*-200*C.
 8. The process of claim 1, wherein the adsorbent isregenerated in a thermal regeneration at about 400*-600*C.
 9. Theprocess of claim 1, wherein the catalyst is applied to the surface ofthe adsorbent in the form of an aqueous solution or suspension in anamount up to 15 percent by weight relative to the weight of theuntreated adsorbent.